1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly, to an electrophotographic image forming apparatus and a method of controlling development by obtaining information concerning consumable replacement, controlling the thickness of a developer on a surface of a developing roller, and controlling the quantity of development on a surface of a photosensitive medium.
2. Description of the Related Art
In general, an electrophotographic image forming apparatus, such as a copier or laser printer, is an apparatus in which an electrostatic latent image is formed on a photosensitive medium, such as a photosensitive drum or photosensitive belt, the electrostatic latent image is developed by predetermined color developers, and the developed image is transferred to a sheet of print paper so that a desired image can be obtained.
Such electrophotographic image forming apparatuses are classified into dry type ones and wet type ones according to developers used therein. A powder toner is used as a developer in the dry type ones and a liquid developer made by mixing a liquid carrier and a toner is used in the wet type ones.
FIG. 1 is a diagram schematically illustrating a structure of a conventional electrophotographic image forming apparatus.
Referring to FIG. 1, the conventional electrophotographic image forming apparatus has a photosensitive medium 10, a charging roller 20, an exposure unit 30, a developing roller 40, a supplying roller 50, and a transfer roller 60.
The photosensitive medium 10 has a structure in which a photosensitive film 12 is formed around the outer circumference of a metallic drum 11. A surface of the photosensitive medium 10 is charged to a predetermined voltage by the charging roller 20, and an electrostatic latent image is formed by light illuminated by the exposure unit 30 on the charged surface of the photosensitive medium 10. In addition, a charge eraser 14 discharging charges on the surface of the photosensitive medium 10, and a cleaning blade 16 removing a remaining toner from the surface of the photosensitive medium 10 are disposed in the vicinity of the photosensitive medium 10.
A predetermined color developer of color developers, for example, a toner, is applied by the developing roller 40 to the electrostatic latent image formed on the surface of the photosensitive medium 10, and, accordingly, the electrostatic latent image is developed as a desired image. At this time, the toner is supplied by the supplying roller 50 from a developer container 52 to a surface of the developing roller 40, and then is transferred to the surface of the photosensitive medium 10 by the developing roller 40. Such transfer of the toner is achieved by a first potential difference between the supplying roller 50 and the developing roller 40 and a second potential difference between the developing roller 40 and the electrostatic latent image formed on the surface of the photosensitive medium 10.
The developed image on the surface of the photosensitive medium 10 is transferred to a print paper P by the transfer roller 60.
However, in the conventional image forming apparatus having the above-described structure, as the accumulated total number of printed papers increases, the quantity of the toner contained in the developer container 52 decreases, and characteristics of the photosensitive film 12 formed on the surface of the photosensitive medium 10 deteriorate. In addition, a thickness of the photosensitive film 12 is gradually reduced since the surface of the photosensitive medium 10 is abraded by the blade 16 cleaning the surface of the photosensitive medium 10. When the quantity of the toner contained in the developer container 52 decreases as mentioned above, the quantity of the toner supplied from the supplying roller 50 to the developing roller 40 is decreased. When the characteristics of the photosensitive film 12 deteriorate, an exposure potential of the electrostatic latent image is changed. When the thickness of the photosensitive film 12 is reduced, a capacitance of the photosensitive film 12 is changed, thereby changing a developing current. When the quantity of development on the surface of the photosensitive medium 10 is changed, there occurs a problem in that concentration of the image transferred to the print paper P becomes inhomogeneous, and the quality of an image deteriorates. Here, the quantity of development is defined as the quantity of a developer per unit area of the surface of the photosensitive medium 10.
Therefore, in the conventional electrophotographic image forming apparatus, even when the quantity of the toner decreases, or the characteristics of the photosensitive film 12 deteriorate, the quantity of development needs to be controlled so that homogeneous concentration of an image can be obtained. In addition, it is necessary to detect whether or not the toner is exhausted, whether the thickness of the photosensitive film 12 is decreased, and the likeso that the developer container 52 can be replenished with new toner and the photosensitive medium 10 can be replaced with a new one in advance.
Although apparatuses and methods of controlling the quantity of development and obtaining information concerning replacement of consumables have been proposed, the apparatuses and methods have drawbacks in that they require many sensors and devices and complex processes.